First, I would like to make it abundantly clear that I've never had so much as a sip of an alcoholic beverage or tried any illicit substances. I tried smoking tobacco a time or two, but I didn't like it, and given my allergies, it's probably not a good idea for me to willingly inhale any smoke. Also, there's the slight fact that tobacco kills many of its users. The only drugs I take on a regular basis are caffeine and ibuprofen (Advil).
That being said, I think people should have the right to place whatever substances in their bodies that they see fit, as long as they do no one else any harm. People currently have the right to get drunk off their asses in this nation, and while I personally think those who do so are idiots, as long as they don't get behind the wheel of a car or play with firearms, sharp objects, or other potentially hazardous materials while in the presence of others, it's their life and their choices to make. I can see no moral or ethical reason that the same reasoning is not used for any other illicit substance. We already have hundreds, if not thousands, of laws against harming people, and those laws should be enforced to the fullest extent of the law. However, we also have hundreds, if not thousands, of laws against people harming themselves, and this is an error the likes of which we haven't seen since Prohibition. Organized crime actually got its major impetus from that failed and long-since overturned amendment to the Constitution of the United States, and the reason for that came down to one word: Money. Where there's money, where there's the potential for profits, where there's people who want a product, there will be people to supply those people and reap those profits. I don't care if you're talking about apples at the local market, gasoline at the local filling station, or illicit substances. The only thing drug criminalization has accomplished is raising the profit margins of the drug dealers and suppliers, removed quality controls, and removed the option of civilized resolution of disputes for those who deal in those substances, which in the 1930s, translated into mobsters using Tommy guns to drive by competing speakeasies, and nowadays, translates into some of the worst of the regular occurrences you see on the news.
Furthermore, an overwhelming majority of people in the U.S., while supporting the "war on drugs", by a not quite as large but still overwhelming majority, believe that it's a "war" that will never be won. So now the questions are thus: "Do we continue to engage in this exercise in futility?" and "If church groups and parent organizations want to prevent youth drug use, what methods work without involving the government?" But that's another debate for another time.